Method for testing an optical investigation system

ABSTRACT

A method for testing an optical investigation system, with an imaging device, a video camera and a light source for optical investigation of an object, a reference surface with predetermined optical properties is illuminated with illuminating light from a light source. An image of the reference surface is recorded by the imaging device and the video camera. An operating condition of the video camera that prevails during the recording of the image is recorded. The functionality or another property of the investigation system is determined on the basis of the recorded operating condition.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority of German patent application No.10 2009 058 662.8 filed on Dec. 16, 2009.

FIELD OF THE INVENTION

The present invention relates to a method for testing an opticalinvestigation system, with a light source, an imaging device and a videocamera, for optical investigation of an object both within and outsidethe field of medicine. The present invention relates in particular to amethod for testing an endoscopy system with a light source, an endoscopeand a video camera

BACKGROUND OF THE INVENTION

Endoscopy systems, consisting of an endoscope and a light source, areused for endoscopy in medical or non-medical applications—in the lattercase also known as boroscopy. The light source can be integrated in theendoscope, in particular in its distal end, or can be present as aseparate unit, which is optically coupled with an endoscope by a lightconductor cable. Light from the light source emerges at the distal endof the endoscope and there illuminates an object to be investigated.Light remitted by the object is captured by a lens on the distal end ofthe endoscope and conducted onto a light-sensitive image sensor orconveyed, for example by means of an oriented bundle of lightwaveconductors or a rod lens system, to the proximal end of the endoscope.In the latter case the light remitted by the object can be observed onthe proximal end of the endoscope by an eyepiece or is recorded by meansof a video camera. As an alternative or in addition to remitted light,light emitted by the object can also be observed, in particularfluorescent light.

The quality of an image recorded by an endoscopy system, in particularbrightness, brightness-color contrast, signal-noise ratio, colorfidelity and resolution or sharpness, depends on the observed object, inparticular its optical properties, and above all on the endoscopysystem. Relevant factors are, for example, the functionality of thelight source, its radiant capacity or the light beam generated by it,the spectrum of generated light, in some cases the transmissionproperties of an employed light conductor cable and the coupling of thelight conductor cable with the light source and with the endoscope, thefunctionality of the light transmission within the endoscope, the degreeof effectiveness of the uncoupling of light from the light source out ofthe endoscope, the functionality or optical properties of theobservation beam path in the endoscope, possibly including an orientedbundle of lightwave conductors or a rod lens system, the functionalityof the eyepiece or video camera. Frequent sources of failure are, amongothers, the light source subjected to an alteration process, possiblythe light conductor cable and its coupling to the light source and theendoscope, and the coupling of a video camera to the endoscope.

Fluorescent light is observed for medical-diagnostic purposes inparticular. In photodynamic diagnostics (PDD), for example, afluorescence of protoporphyrin IX induced by administered5-aminolevulinic acid (ALA) is observed. Enrichment of ALA and thus alsothe intensity of the fluorescence depend on the condition of the tissue.In autofluorescence diagnostics (AF diagnostics) the fluorescence ofbodily-produced fluorophores is observed, whose concentration islikewise dependent on the condition of the tissue. Fluorescentdiagnostic methods are used in fields other than medicine as well.

To prevent remitted excitation light or illuminating light fromoutshining the fluorescence, an illumination filter is used in theillumination or excitation beam path between light source and object andin the observation beam path between object and video camera oreyepiece. The illumination filter is a short pass filter, whichessentially transmits only the short wavelengths required to excite thefluorescence, but on the other hand primarily or almost exclusivelyreflects or absorbs longer wavelengths. A very reduced, but notdisappearing, transmission in the blocking range is desired with manyapplications in order to receive, even without fluorescence, an imagethat has a low brightness but is visible. The observation filter is along pass filter that transmits only wavelengths of fluorescence andreflects or absorbs short-wave illuminating light remitted by theobject. Illumination or excitation filters can as a rule be manually ormechanically exchanged or changed. Observation filters can bereplaceable or changeable, but in many cases are firmly built into theendoscope. In urology, for example, for observation in white light, ALAor AF fluorescence, various endoscopes are used that, at least in theobservation beam path, are optimized for their respective use or have acorresponding filter characteristic. The aforementioned sources offailure or influences on functionality of the endoscopy system include,in the case of observation of fluorescence, the combination of theillumination filter or spectrum of the light source on the one hand andof the observation filter on the other hand.

A corresponding problem exists with other optical investigation systems,which include an imaging device, a light source and a video camera foroptical investigation of medical and non-medical objects in remittedlight and/or in fluorescent light. These include exoscopes, which forinstance are used for diagnostics and for microsurgical procedures on orclose to bodily surfaces.

DE 196 38 809 A1 describes a device for testing and/or adjusting a PDDor PDT (photodynamic therapy) system and/or for training on a system ofthis type. Positioned in a housing is a target, opposite to which adistal end of an endoscope can be mounted. The curvature of the targetcan correspond to the variable field curvature of an imaging unit of theendoscope. A photo element and light sources are provided in the target.The photo element records the illuminating strength of an excitationlight emitted from the endoscope. A control unit guides the lightsources as a function of the illuminating strength recorded by the photoelement.

DE 198 55 853 A1 describes an apparatus for testing and/or adjusting aPDD or PDT system and/or for training on a system of this type. Theapparatus includes a luminescent phantom with a fluorescent dye. One endof an endoscope can be positioned opposite the luminescent phantom.

In the post-published DE 10 2009 043 696, an apparatus and a method fortesting endoscopes are described. The apparatus includes a filter modulewith several perforations in which optic filters are positioned. Thefilter module is illuminated from one direction by the light source viaa light conductor cable. From an opposite direction the lighttransmitted by the filter module is observed by means of an endoscope.

Each of the apparatuses and methods known by now, depending on concretetask assignments arising in practice, have advantages and disadvantages.For example, under some conditions and for a few applications none ofthe described apparatuses and methods allows a reliable testing of acomplete endoscopy system or of a different complete opticalinvestigation system in precisely the condition in which it was used oris used medically or non-medically before or afterward.

A disadvantage of the apparatuses and methods described in DE 196 38 809A1 and in DE 198 55 853 A1 consists in the fact that the video cameraautomatically post-controls a minor erroneous image brightness, so thatit is partially or completely compensated by the camera system and onlyat very reduced lighting does the image become recognizably poor.Something similar occurs with the human eye. In particular influorescent diagnostics, however, the risk of an incorrect diagnosis, inparticular the overlooking of a tumor, exists immediately beforehand.

SUMMARY OF THE INVENTION

An object of the present invention consists in providing an improvedmethod for testing an optical investigation system.

This object is fulfilled by the content of the independent claims.

Refinements are indicated in the dependent claims.

Embodiments of the present invention are based on the idea of recordingor calling up an operating condition of a video camera of an opticalinvestigation system in the context of a test method and, on the basisof the recorded operating condition, of determining the functionality oranother property of the optical investigation system. In many videocameras the operating condition is selected, depending on the existingexposure situation, by the image sensor itself or by a camera controlunit (CCU) positioned inside or outside the camera. The operatingcondition here includes in particular the exposure time as well as thegain factor or other parameters of an analog signal gain in the imagesensor. By appropriate algorithms, the exposure time and gain factor,for example, are selected in such a way that the median brightnessvalues of the recorded image (in the form of an existing analog ordigital electric signal) or the brightness values of a prioritized area(for example, in the center of the image) of the recorded image assume apredetermined value.

In a light-sensitive image sensor (for example, CCD or CMOS sensor), asa rule, both the exposure time and the analog gain of the electricsignals can be selected before their digitization. The longest possibleexposure time is thus predetermined by the image repetition frequency.If the image generated by the imaging lens on the image sensor isbright, a short exposure time and a low or minimal gain are selected.With decreasing image brightness, the exposure time is extended, forexample, at first at unchanged low gain, to achieve the lowest possiblenoise. The longest possible exposure time at an image repeatingfrequency of 50 Hz (50 whole or half images per second) amounts tosomething less than 20 ms. If the exposure time cannot be furtherextended, the gain is increased. Thus with decreasing brightness of theimage on the image sensor, the noise increases or the signal-noisedistance in the signal of the image sensor decreases. When the gain hasreached a maximum value with decreasing brightness of the image on theimage sensor, only the brightness values of the digitized image canstill be numerically scaled. Consequently, with further decreasingbrightness the image quality is drastically reduced.

In the described example, with the video camera in operating condition,three stages can be distinguished.

At stage 1 the gain assumes a low, in particular a minimal, value.Alternatively the gain is selected at another predetermined value, forexample an average value. Within stage 1 a variation in brightness iscompensated by a variation in exposure time. Stage 1 is also designatedas auto shutter mode.

In stage 2 the exposure time has the maximum value possible at the givenimage repetition frequency. Within stage 2 a variation in brightness ofthe image on the image sensor is compensated by a variation in gain.Stage 2 is also referred to as AGC (auto gain control) mode.

In stage 3 the maximum exposure time and maximum gain are reached.Within stage 3 a variation in brightness of the image on the imagesensor has a variation in brightness values of the digital image as aconsequence. They can be improved only by a numerical scaling. Here, notonly the signal-noise distance decreases, but also the resolution of thebrightness values.

For many applications, stage 1 is suited without restriction, whilestage 2 is appropriate only with restrictions or up to a certainthreshold value of gain and stage 3 is not appropriate. When stage 1 isreached, the optical investigation system is functional withoutrestriction. The radiant power of the light source, possibly the qualityof the light conductor cable and its coupling to the light source andendoscope as well as the additional illumination beam path andobservation beam path are sufficient in view of the given degree ofreflectance of the observed object and its distance from the imagingdevice.

Within stage 2 the noise in the digitized image recorded by the imagesensor increases or the signal-noise distance decreases. The quality ofthe recorded image, however, can nevertheless be sufficient for apredetermined application within the entire stage 2 or up to a thresholdvalue of the gain. In stage 3 the quality of the image recorded by theimage sensor is no longer sufficient for many applications and inparticular for medical applications.

These results can be obtained without absolutely measuring theindividual parts of the optical investigation system, for example lightsource, light conductor cable, endoscope, video camera and theirparticular coupling. In particular, therefore, no calibrated measuringdevices are required either. In addition, the optical investigationsystem can be tested in precisely the condition in which it can be usedbefore or after the testing for optical investigation of an object. Inparticular, also, no light conductor cables or other connections foroptical or electrical coupling are required to be severed, modified orconverted. In addition, no calibration of the video camera is requiredbecause no absolute measurement of the brightness of the image on theimage sensor of the camera is necessary, but rather it is possible todraw conclusions immediately from the operating condition of the cameraconcerning the functionality of the optical investigation system.

In addition to the exposure time and gain, additional parameters can bevaried to adapt to an exposure situation that departs from the describedexample. For example, automatically controlled by the CCU or fromoutside, the image repetition frequency and thus the maximum exposuretime can be varied and/or groups of a varying number of image points canbe combined to achieve an improvement of the signal-noise distance withreduced spatial resolution. Both parameters can be varied, for example,simultaneously with the gain within stage 2 or in one or two additionalstages between stage 2 and stage 3.

For a more precise and quantitative description of the operatingcondition of the video camera, an exposure parameter E can be computedfrom the exposure time T and the gain G, for example on the basis of theformula E=a·T^(b)·G^(c). The constants a, b and c result, for example,from geometry, sensitivity and other properties of the video camerasystem and from a normalization of the exposure parameter E, so that forexample in the maximum exposure time and the minimal gain the exposureparameter is E=1. The constants b, c each lie, for example, between 0.3and 3, in particular between 0.5 and 2. In the simplest case, b=c=1 andthus E=a·T·G.

Depending on the structure and functioning of the video camera, forvarious areas of the image sensor or for various areas of the imagerecorded by the video camera or for various color channels, equal ordifferent operating conditions can exist. In testing the opticalinvestigation system, one or more areas or color channels can beselected in this case or the operating conditions of the video camera invarious areas or color channels can be linked with one another logicallyor algebraically.

Instead of recording the operating condition of the video camera bycalling up the existing parameters, the operating condition can also berecorded by determining the noise level or the signal-noise distance inthe recorded image. The noise level is, for example, essentiallyconstant within the stage 1 described above and increases within stages2 and 3 with decreasing brightness of the image on the image sensor.Therefore the operating condition of the video camera can also berecorded by the noise level when the aforementioned parameters are not,or are only partly, called up directly or callable directly.

In a method for testing an optical investigation system with a lightsource, an imaging device and a video camera for optical investigationof an object, a reference surface with predetermined properties isilluminated with illuminating light from a light source. An image of thereference surface is recorded by means of the imaging device and videocamera. An operating condition of the video camera, which is inexistence during the recording of the image, is recorded. Thefunctionality or another property of the investigation system isdetermined on the basis of the recorded operating condition.

The optical investigation system is in particular an endoscopy systemfor medical or technical, non-medical, applications, where the imagingdevice is an endoscope. Endoscopes for non-medical applications are alsodesignated as boroscopes. The video camera can be present in the form ofa separate unit, optically coupled with the imaging device.Alternatively, the video camera can be, for example, integrated into theimaging device.

The reference surface and its optical properties are, in particular,unchangeable or stable over time. The reference surface can approximatea Lambertian radiator, or reflect incident light in a manner thatapproximates ideal diffusion. The light source can be integrated intothe imaging device, for example in the form of a light diode on thedistal end of an endoscope. Alternatively, the light source can beexecuted as a separate device that, for example, is coupled by a lightconductor cable with the imaging device or whose light is conducted byother means onto the object that is to be investigated or onto thereference surface.

The described test method makes possible a simple and rapid testing ofthe functionality of an optical investigation system. Calibrated orgauged measurement apparatuses are not required.

The described test method is applicable in many cases to an opticalinvestigation program in the condition in which it has been or will beput to use before or afterward, for example in medical diagnostics. Withthe described test method it is therefore possible, for example, toestablish simply and rapidly whether all components of the investigationsystem are coupled with one another functionally and perfectly. Forexample, an insufficient optic coupling of an external light source,executed as a separate device, with an endoscope has an impact on theillumination of the object to be investigated or of the referencesurface because of a defective light conductor cable or a faulty plug-inconnection. The insufficient illumination also has an effect on theoperating condition of the video camera and can therefore be recognizedwith the described test method.

With a method as described here the distal end of the imaging device canbe positioned at a predetermined position, in particular also in apredetermined direction, relative to the reference surface and can be insuch position during the illumination and recording of the image. Thisarrangement at a predetermined position and possibly in a predetermineddirection can be supported by a positioning device, which guides andholds the imaging device, and in particular its distal end.Alternatively, for example on the reference surface, one or moreoptically recognizable marks can be placed, so that the distal end ofthe imaging device is positioned relative to the reference surface insuch a way that the marks lie at predetermined sites in the recordedimage, for example on the edge. These marks can simultaneously take overother functions, for example the focusing of the imaging device on thereference surface or—in particular because of its spectralproperties—can simplify the identification of illumination andobservation filters of the optical investigation system.

The arrangement of the distal end of the imaging device at apredetermined position and possibly in a predetermined directionimproves the precision with which the optical investigation system canbe tested. For this purpose the predetermined position and possibly thepredetermined direction correspond, for example, to the typical distanceor to a maximum distance between the distal end of the imaging deviceand the observed object in an application foreseen for the opticalinvestigation system.

In every one of the methods described here, in addition, it is possibleto record an application foreseen for the optical investigation systemand to ascertain a requirement associated with the foreseen applicationof the optical investigation system. A requirement is associated withevery application in such a way that the functionality of the opticalinvestigation system for the application or another predeterminedproperty of the optical investigation system prevails if the operatingcondition that prevails during the recording of the image of thereference surface corresponds to the associated requirement. Forexample, medical-diagnostic investigations in body cavities of varioussize or of organs with various optical properties can place variousdemands on the optical investigation system. These various demands canbecome apparent because of various requirements for the operatingcondition of the video camera that prevails during the recording of theimage of the reference surface.

In every one of the methods described here, the reference surface can beilluminated with irradiance or with an illuminating strength that isequal to a predetermined fraction of the irradiance applied in theforeseen application of the optical investigation system. This isachieved, for example, by dimming the light source or by using adiaphragm, grid or filter. Because of this reduced irradiance, it ispossible to take into account the fact that the object observed in theforeseen use of the optical investigation system has a lesser remissionfactor than the reference surface. Therefore, to execute the testmethod, not only can the reference surface be adapted to the foreseenuse of the optical investigation system that is to be tested, butalternatively the irradiance of the reference surface can be adapted tothe foreseen use, so that the second way can be simpler, depending onthe light source and its control device. The methods described hereallow in this way a highly differentiated testing of an opticalinvestigation system.

In every one of the methods described here, the recording of theoperating condition can include ascertainment of an exposure parameter,and the determination of the functionality or of another property caninclude comparison of the ascertained exposure parameter with apredetermined threshold value. The exposure parameter E, for example, iscalculated according to the formula E=a·T^(b)·G^(c) already described onthe basis of exposure time T and gain G. In comparison to thedifferentiation of the operating condition by stages as also describedabove, calculation of an exposure parameter permits a more precisequantification and finer differentiation. The threshold value, forexample, depends on the foreseen use of the optical investigationsystem. By the choice of the threshold value, for example, it ispossible to take into account the optical properties of an object to beobserved in the foreseen use of the optical investigation system, inparticular the remission factor, the fluorescence-quantity yield and itswavelength dependency, as well as contrasts, and its differences withrespect to the reference object.

In every one of the methods described here, the reference surface can beilluminated successively with illuminating light with a firstillumination spectrum and with illuminating light with a secondillumination spectrum. A first operating condition of the video camera,which prevails during the recording of an image with illumination of thereference surface with the illuminating light with the firstillumination spectrum, and a second operating condition of the videocamera that prevails during the recording of an image with illuminationof the reference surface with the illuminating light with the secondillumination spectrum are recorded. The functionality or anotherproperty of the optical investigation system is determined on the basisof the first operating condition and the second operating condition.This can be especially useful when the optical investigation system isto be used to record fluorescence (for example in PDD or in AFdiagnostics).

For example, the light source, by filters that can be inserted manuallyor mechanically into the illumination beam path, is configured toprovide alternatively a spectrum, which is at least approximately white,of visible light and one or more spectra to excite fluorescence ofvarious fluorophores. If the use foreseen for the optical investigationsystem calls for the recording of fluorescent light, the imaging devicemust comprise an observation filter or a corresponding filtercharacteristic, which is adapted to the spectrum of the illuminatinglight or to the illumination filter. By illuminating the referencesurface with illuminating light with various spectra and recording theoperating condition of the video camera that prevails in each case, itis possible to ascertain which observation filter or which filtercharacteristic is comprised by the observation beam path of the imagingdevice. This makes possible a simple, rapid and reliable verification asto whether the optical investigation system includes the correctobservation filter or the correct imaging device with the correct filtercharacteristic of the observation beam path.

In every one of the methods described here, in addition, it is possibleto record a first operating condition of the video camera during therecording of an image of the reference surface while using a firstobservation filter or an imaging device with a first filtercharacteristic of the observation beam path and to record a secondoperating condition of the video camera during the recording of a secondimage while using a second observation filter or an imaging device witha second filter characteristic of the observation beam path. On thebasis of the two operating conditions, the illumination spectrum or theemployed illumination filter can be determined. Thus, for example, theerror-free functioning of a mechanical control unit of the illuminationfilter can be verified or a manually applied illumination filter can beidentified.

By recording several operating conditions of the video camera whilerecording images using various illumination filters and/or observationfilters, additional detailed information can be obtained on propertiesof the optical investigation system. To the extent that the illuminationfilter or observation filter can be controlled and reproduciblyexchanged, it is possible to draw unequivocal conclusions concerning therespective other filter and/or the functionality of a device forexchanging the filter.

In every one of the methods described here, in which several operatingconditions are recorded with various illumination filters and/or withvarious observation filters, the determination of the functionality orof another property of the optical investigation system can includeascertainment, in particular a computation, of an indicator parameterfrom the recorded operating conditions and a comparison of theascertained indicator parameter with one or especially several thresholdvalues. For example, an exposure parameter is ascertained from each ofthe recorded operating conditions, as described above. The exposureparameters are then logically or algebraically linked, for example byforming a ratio or a difference, which forms the indicator parameter.

In every one of the methods described here, the recording of anoperating condition can include recording of one operating condition foreach of a number of color channels. In addition, recording of anoperating condition can include ascertaining of an exposure parameterfor each of the number of color channels. This is particularly true whenthe video camera being used foresees or makes possible the independentselection of various exposure times and/or gains for various colorchannels. The recorded operating conditions or exposure parameters,which are associated with various color channels, can in turn belogically or algebraically linked and then compared, for example with athreshold value, to determine functionality or another property of theoptical investigation system. In particular, the recorded operatingconditions or exposure parameters are logically or algebraically linkedand then compared with several threshold values.

In every one of the methods described here, the recording of anoperating condition can include recording of a white balance parameter.White balance parameters can be obtained or selected during an ongoingmanual or—automatically or manually triggered or controlled—automaticwhite balance. White balance parameters describe or determine, forexample, the proportions of exposure times, gains or exposure parametersof the individual color channels or constitute correction factors thatare to be applied during or after digitization of the image. On thebasis of the white balance parameters, for example, it can be easily andreliably determined whether the illuminating light from the light sourceis (approximately) white or includes predominantly short wavelengths forexciting fluorescence.

Depending on the optical properties of the reference surface, moredetailed information on the properties of the investigation system, inparticular illumination filters and observations filters, can beobtained on the basis of the operating conditions or exposure parametersassociated with the individual color channels or on the basis of one ormore white balance parameters.

The reference surface in each of the methods described here can be whiteor gray, or can have a remission factor that is essentially wavelengthindependent, especially within the spectral range visible to the humaneye. Alternatively, the reference surface can be colored or can have awavelength dependent remission factor. Alternatively or in addition, thereference surface can be fluorescent. The reference surface can haveunified or homogeneous optical properties or can include areas withdifferent optical properties. As is described hereinafter with referenceto the drawings, a reference surface having several areas with differentoptical properties can make possible an even more detailed or moreprecise determination of properties of the optical investigation system.

In every one of the methods described here, the recording of anoperating condition can include recording of a noise level or of asignal-noise distance in the recorded image. From the noise level, asalready described, conclusions can be drawn about the operatingcondition of the video camera. Thus the operating condition of the videocamera can also be recorded if the parameter or parameters thatdetermine it cannot be directly acquired or are not otherwiseaccessible.

In every one of the methods described here, in addition, patient datacan be recorded and information on the functionality or on anotherproperty of the optical investigation system and the patient data can befiled in a database. By integrating the test method with the recordingand storage of patient data, it is possible to ensure that with everymedical-diagnostic application of the optical investigation system, saidsystem is tested with respect to its functionality and/or to anotherproperty and the result of the testing is documented individually or inrelation to the patient. The test method can thus become a reliable,non-manipulatable component of quality assurance in everyday clinicalpractice.

In every one of the methods described here, after determination of thefunctionality or of another property of the optical investigationsystem, a report can be displayed. This report reveals the functionalityor the degree of functionality and/or of another determined property ofthe investigation system. Alternatively or in addition, the report cancontain an operating instruction or an operating recommendation. Forexample, the report can include a demand to check plug-in connectionsbetween a light conductor cable and the light source or imaging deviceor to exchange the imaging device or an observation filter and then torepeat the testing of the optical investigation system. After repeatedestablishment of faulty functionality, other instructions orrecommendations can be reported, for example a recommendation ofimmediate or prompt replacement of the light source.

The present invention can be implemented as a method or as a computerprogram with program code for executing or control of such a method ifthe computer program runs on a computer or processor. In addition, theinvention can be implemented as a computer program product with aprogram code stored on a mechanically readable carrier (for example, anROM, PROM, EPROM, EEPROM or Flash storage device, a CD-ROM, DVD, HD-DVD,Blue Ray DVD, diskette or hard drive) or in the form of firmware forexecuting one of the aforementioned methods if the computer programproduct runs on a computer, calculator or processor. In addition thepresent invention can be implemented as a digital storage medium (forexample, ROM, PROM, EPROM, EEPROM or Flash storage device, CD-ROM, DVD,HD-DVD, Blue Ray DVD, diskette or hard drive) with electronicallyreadable control signals that can interact with a programmable computeror processor system in such a way that one of the described methods isexecuted.

In addition the present invention can be implemented as a control devicefor an optical investigation system with an imaging device, inparticular an endoscope, a video camera and a light source for opticalinvestigation of an object, where the control device is configured toexecute one of the described methods, or where the control deviceincludes a computer program, a computer program product or a digitalstorage medium, as described in the preceding paragraph. The controldevice can be a video camera control or can be integrated therein.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are explained in more detail hereinafter with reference tothe drawings.

FIG. 1 shows a schematic depiction of an optical investigation system.

FIG. 2 shows a schematic depiction of an endoscope with a testapparatus.

FIG. 3 shows a schematic depiction of several spectra.

FIG. 4 shows a schematic depiction of additional spectra.

FIG. 5 shows a schematic depiction of products of transmission spectra.

FIG. 6 shows a schematic depiction of white balance parameters.

FIG. 7 shows a schematic depiction of additional white balanceparameters.

FIG. 8 shows a schematic depiction of a flow diagram.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a schematic depiction of an optical investigation system.The optical investigation system in this example is an endoscopy system,which can be applied, for example, in medical-diagnostic methods inurology and in other specialties. The endoscopy system includes anendoscope 10 with a proximal end 11 and a distal end 12. The endoscope10 includes an illumination or excitation beam path and an observationbeam path, which are not shown in detail in FIG. 1. The illuminationbeam path includes in particular one or more lightwave conductors totransmit illumination or excitation light from the proximal end 11 tothe distal end 12 and a light outlet on the distal end 12 through whichillumination light can exit from the distal end 12 of the endoscope 10in order to illuminate an object to be observed. The observation beampath includes a light inlet on the distal end 12 of the endoscope 10, alens to transmit observation light emitted from an observed object, fromthe distal end 12 to the proximal end 11, an observation filter 13 andan eyepiece 14. To transmit the observation light from the distal end 12to the proximal end 11 of the endoscope 10, a rod lens system, forexample, or an oriented bundle of lightwave conductors is provided in ashaft 17 of the endoscope 10. The endoscope 10 in addition comprises onits proximal end 11 a coupling 15 for mechanical and optical coupling ofa light conductor cable 19 with the described illumination beam path inthe endoscope 10.

The endoscope 10 is coupled with a light source apparatus 20 by thelight conductor cable 19. The light source apparatus 20 includes a lightsource 22, for example a halogen lamp, a high-pressure gas dischargelamp, a light diode or a laser. In addition the light source apparatus20 includes a first converging lens 23, an illumination filter 24 and asecond converging lens 25. The light source 22 is coupled with the lightconductor cable 19 by the first converging lens 23, the illuminationfilter 24, the second converging lens 25 and a coupling 26.

A video camera 31 is coupled mechanically or optically by the eyepiece14 with the endoscope 10 and its observation beam path. The video camera31 includes a light-sensitive image sensor, for example a CCD or CMOSsensor, to convert light falling onto the image sensor into analog ordigital electrical signals. By means of a signal cable 33, the videocamera 31 is coupled with a camera control unit 35, designated as CCU,to transmit analog or digital electrical or optical signals.

The light source apparatus 20, camera control unit 35, and a screen 37are coupled with one another by a communication bus 39 or severalseparate signal lines. By means of the communication bus 39, additionalapparatuses, not shown in FIG. 1, can be coupled with the light sourceapparatus 20, the camera control unit 35 and the screen 37 inside oroutside the treatment area in which the endoscope system is installed;examples include a database, a keyboard, a computer mouse and other userinterfaces.

Also shown in FIG. 1 is a test apparatus 40 with a light-insulatedhousing 41, a hollow space 42 in the light-insulated housing 41 and anaperture 43 to the hollow space 42. The distal end 12 of the endoscope10 is introduced through the aperture 43 into the hollow space 42 of thetest apparatus 40. A positioning device 50 located in the aperture 43holds the shaft 17 of the endoscope 10 by form-locking or force-fitting,in such a way that the distal end 12 of the endoscope 19 is positionedin a predetermined position and in a predetermined direction in thehollow space 42. In addition, the positioning device 50, at least whenthe shaft 17 of the endoscope 10 is mounted in the positioning device50, to a great extent prevents the penetration of light from theenvironment through the aperture 43 into the hollow space 42 in thehousing 41.

In addition, a reference body 70 with a reference surface 72 ispositioned in the hollow space 42 of the test apparatus 40. Thereference surface 72 has predetermined optical properties and thespatial shape of a portion of a spherical surface or of a cylindricalmantle. The position foreseen for the distal end 12 of the endoscope 10is situated in particular at the center point of this spherical surfaceor on the axis of symmetry of the cylindrical mantle. In particular, themain point on the object side, or the point of intersection of theoptical axis with the object-side principal plane of the imaging device10, stands at the center point of the spherical surface or on the axisof symmetry of the cylindrical mantle.

The reference surface 72 has predetermined optical properties that areunchangeable or stable over time. The reference surface 72 can be whiteor can have a remission factor that is essentially wavelengthindependent in the spectral range visible to the human eye. Thereference surface 72 can alternatively be in color or can have awavelength dependent remission factor in the spectral range visible tothe human eye. Alternatively or in addition, the reference surface 72can be fluorescent. Here the wavelengths that are required forexcitation of fluorescence, are situated for example, in the ultravioletor, preferable for medical applications, in the blue spectral range andthe emitted fluorescent light is in the green, red or infrared spectralrange. The optical properties can be homogeneous or location-independentover the entire reference surface 72.

Alternatively the reference surface comprises several areas with variousoptical properties. In the example shown in FIG. 1, the referencesurface 72 is predominantly white with an indicator area 75 and areference area 76, which each have optical properties that differ fromthose of the rest of the reference surface 72. The indicator area 75 andreference area 76, with sharp edges or on the basis of their arrangementor shape, can simplify or make possible a focusing or a selection of thefocal distance or size of the field of vision of the imaging device. Inaddition the optical properties of the indicator area 75 and of thereference area 76 can simplify a determination of the transmissionspectrum of the illumination filter 24 and of the transmission spectrumof the observation filter 13. The reference body 70, apart from theindicator area and the reference area 76 on the reference surface 72,consists in particular of polytetrafluorethylene PTFE, which inparticular is marketed by DuPont under the brand name Teflon, or ofsilicon. Both PTFE and silicon can be filled with white or coloredpigments or dyes.

FIG. 2 shows a schematic axonometric view of an endoscope 10 and of atest apparatus 40 that are similar to the endoscope and test apparatusthat were presented above with reference to FIG. 1. Contrary to FIG. 1,no separate light source, video camera or other apparatuses are shown.The exact positioning of the distal end of the endoscope 10 in the testapparatus 40 is achieved in this example by form-locking between thepositioning device 50 and the distal end 11 of the endoscope 10, inparticular by means of a mechanical stop or a catch-locking connection.

The test methods described hereinafter are also applicable to opticalinvestigation systems and test apparatuses that differ from thoseillustrated in FIGS. 1 and 2. For example, the test methods areapplicable regardless of whether a light source and/or a video cameraare separate units that can be coupled with the endoscope or areintegrated in the endoscope at its proximal or distal end. In addition,the test methods are applicable when the excitation or illuminatinglight is conducted not by the endoscope or generally by the imagingdevice, but rather in other manner onto the object to be observed oronto the reference surface. The arrangement of illumination andobservation filters can also differ from the examples presented abovewith reference to FIGS. 1 and 2. For the sake of greater clarity,reference numbers from FIGS. 1 and 2 are nevertheless used hereinafterby way of example.

In a first test method for an optical investigation system, the distalend 12 of an imaging device 10 is inserted into a hollow space 42 in ahousing 41 of a test apparatus 40. A positioning device 50 holds theimaging device 10, in particular its distal end 12, by force-lockingand/or form-locking at a predetermined position and in a predetermineddirection relative to a reference surface 72. The reference surface isin particular white or has a remission factor that is essentiallywavelength independent within the spectral range visible to the humaneye.

The reference surface 72 is then illuminated with illuminating lightfrom a light source 22. In addition to the spectral properties of thelight source 22, an illumination filter 24 in the illumination beam pathdetermines the spectrum of the illuminating light. The illuminationfilter 24 can be inserted manually or mechanically into the illuminationbeam path and removed from it. As a rule, several illumination filters24 are available that can be inserted in alternation into theillumination beam path. The light source 22 generates, for example, aspectrum that is perceived as white by the human eye. If no illuminationfilter 24 is positioned in the illumination beam path, the referencesurface 72 is thus illuminated with white light.

First an illumination filter 24 is inserted that is appropriate for theforeseen application of the optical investigation system. If the opticalinvestigation system is foreseen for observing an object in white lightand the light source 22 generates white light, no illumination filter isinserted into the illumination beam path.

In illuminating the reference surface 72 with illuminating light of theforeseen spectrum, a white balance of the video camera 31 can beexecuted. This white balance can occur manually or automatically, sothat an automatic white balance can be controlled or triggered manuallyor automatically. In the white balance, two white balance parameters,for example, are determined, which are also known as white balance gains(WBG). The first WBG parameter determines the proportion of the gains inthe red and green color channels; the second WBG parameter determinesthe proportion of the gains in the blue and green color channels. Thegains are analogous gains before digitization by electric signalsarising primarily in the image sensor. Alternatively the WBG parametersdetermine, for example, the proportion of corrector factors, which areto be applied to digitized signals of the individual color channels.

The described white balance is optional. In many cases, however, it isrequired or meaningful in order to achieve a natural color impression ina successive application of the optical investigation system. The whitebalance parameters constitute a part of the operating condition of thevideo camera 331. If the described white balance is executed,conclusions can be drawn from the values of the white balance parametersconcerning properties of the optical investigation system. This isdescribed hereinafter in greater detail with reference to FIGS. 6 and 7.

If the reference surface 72 is not homogeneously white or does not havea remission factor that is wavelength independent for the human eye atall sites, one or more white areas of the reference surface 72 can beselected manually or automatically for the white balance. If a whitebalance is performed on a non-white reference surface 72 or on anon-white area of the reference surface 72, conclusions can likewise bedrawn from the resulting white balance parameters concerning propertiesof the optical investigation system.

In illuminating the reference surface 72 with the foreseen illuminatinglight, an image of the reference surface 72 is generated by means of theimaging device 10. This image in illuminating light remitted by thereference surface 72 and in some cases in fluorescent light emitted bythe reference surface 72 is spectrally filtered by an observation filter13. The image generated by the imaging device 10 and in some casesfiltered by the observation filter 13 is visually recorded or observedby an eyepiece 14 or recorded by a video camera 31. In recording theimage, the video camera 31 itself or the camera control unit 35 selectsan operating condition of the video camera 31 in such a way that therecorded image or the analog or digital electric signals correspond topredetermined requirements. These requirements include, for example, apredetermined median value of the brightness values in the entirerecorded image or in a partial area of the recorded image. The exposuretime and the (especially analog) gain of the primary electric signalsbefore their digitization are the parameters that make up or describethe operating condition of the video camera 31, and typically areselected depending on the brightness of the optical image generated bythe imaging device 10 on the image sensor of the video camera 31. Boththe exposure time and the gain can have the same values for all imagepoints and all color channels or can have different values for differentcolor channels or different areas of the image sensor.

In illuminating the reference surface 72, one or more parameters of theautomatically selected operating condition of the video camera arerecorded, for example by scanning or reading out from a storage device.On the basis of the recorded operating parameters of the video camera31, conclusions can be drawn concerning the exposure situation, inparticular the brightness, of the optical image generated by the imagingdevice 10 on the image sensor of the video camera 31. Minimum valuesexist for this brightness that can be dependent on the expectedapplication of the optical investigation system. The optical imagegenerated by the imaging device 10 on the image sensor of the videocamera 31 fulfills the requirements and is in particular sufficientlybright, when there is completely correct configuration of the opticalinvestigation system and in particular if all components are connectedor coupled with one another with complete functionality and withouterror and if both the illumination and the observation filterscorrespond to the expected application.

If the operating condition of the video camera 31 fulfills apredetermined requirement (for example, to lie in stage 1 as describedabove) it can be concluded that there is an unrestricted functionalityof the optical investigation system. If the recorded operating conditionof the video camera 31 does not correspond to the predeterminedrequirement (for example, lies in either of steps 1 or 2 as describedabove), it can be concluded that the optical investigation system is notfunctional, or is not functional without restriction. For example, thelight source 22 delivers too low a beam of light, the light conductorcable 19 is defective or not coupled perfectly with the light source 22or the imaging device 10, the imaging device 10 is defective, a wrongillumination filter is positioned in the illumination beam path, or awrong observation filter is positioned in the observation beam path.

The application for which the optical investigation system is intendedcan be recorded at any desired time before comparing the recordedoperating condition of the video camera 31 with the predeterminedrequirement. For this purpose, in particular, an entry at a userinterface is recorded after a corresponding demand. Because differentapplications of the optical investigation system make different demandson the quality of the recorded images, various requirements concerningthe required operating condition can be associated with variousapplications. The requirement that must be met by the recorded operatingcondition of the optical investigation system is ascertained as therequirement associated with the recorded expected application. Therequirement includes, for example, one or more threshold values for theoperating condition, in particular threshold values for the exposuretime, for the gain or for an exposure parameter calculated from it.

After the described determination of the functionality of theinvestigation system for the expected application, a correspondingreport can be issued via a user interface. This report can includeoperating instructions or operating recommendations. For example, if theoperating condition does not meet the requirement, a demand is issued totest the components of the optical investigation system and theircoupling or to exchange the light source 22 or another component and torepeat the test process.

The precision of the described test method can be increased, forexample, by computing an exposure parameter from the operating conditionof the video camera, in particular from the exposure time, the gainand/or additional parameters. The exposure parameter E is computed, forexample, according to the already mentioned formula E=a·T^(b)·G^(c). Onthe basis of the exposure parameter, a detailed account of thefunctionality of the optical investigation system and a more preciseoperating recommendation can be expressed. For example, it becomespossible to distinguish whether the optical investigation system issuitable without restriction, with restriction, or not suitable at all.The exposure parameter can be filed or stored. On repeated testing ofthe same optical investigation system, a trend or a development of theexposure parameter over time can be ascertained, which for example canbe traced back to an ageing process of the light source 22. From thestage of the ageing process of the light source 22, a recommendation isgiven, for example, to exchange it or to adopt restrictions in operatingthe light source 22.

In the framework of the described test method, in particular by a userinterface, patient data can be recorded and then filed in a databasealong with the result of the test method and in particular with theresult of an ensuing examination of the patient by means of the opticinvestigation system. This ensures that the optic investigation systembefore or after the examination of a patient is tested for itsfunctionality and that the result of this test is logged or documented.

The requirements or threshold values, which are associated with thevarious applications of the optical investigation system, for theoperating condition or for the parameters that characterize theoperating condition, can be determined empirically in that medicalpersonnel conduct investigations that correspond to the expectedapplication under real conditions or with various illuminationsituations and evaluate the quality of the image of the observed object.

An object that is to be observed in an expected application of theoptical investigation system can have a remission factor and otheroptical properties that differ from those of the reference surface 72.During the test process described above, this can be taken into accountby changing or adjusting the brightness of the light source 22 duringthe test process, for example by dimming or by the use of a diaphragm,grid or filter. In particular, the available light flow is reduced by afactor that corresponds to the ratio between the remission factor of anobject relevant in the expected application of the investigation systemand the remission factor of the reference surface 72.

If the video camera 31 being used so allows, in the test methoddescribed above either the exposure time or the gain can be firmly setin advance and only the respective other parameter that is beingselected can be recorded and evaluated corresponding to the descriptiongiven above.

Hereinafter, other variants of the test method described above arepresented, which are applicable, for example, when the expectedapplication of the optical investigation system is PDD, AF diagnosticsor another fluorescence diagnostics. For clarification, fluorescenceexcitation and de-excitation and transmission spectra of illuminationand observation filters for the fluorescence diagnostics are describedfirst. For example, the filters used for PDD and for AGF diagnosticsdiffer from one another, but are easily interchangeable in visualobservation. The test method described above can be modified in such away that the filters in use can be identified.

FIG. 3 shows a schematic depiction of a fluorescence excitation spectrum81L and of a fluorescence de-excitation spectrum 82L from fluorescenceof protoporphyrin IX induced by 5-aminolevulinic acid (ALA). Thewavelength lambda is assigned to the abscissa axis and quantity yield orintensity to the ordinate axis in arbitrary units. Also depicted are atransmission spectrum 83L of an appropriate illumination filter 24 and atransmission spectrum 84L of an appropriate observation filter 13. Forthe transmission spectra 83L and 84L, the transmittance degree in eachcase is assigned to the ordinate axis.

In addition, the product 87 of transmission spectra 83L, 84L or thetransmission spectrum of the successively switched-on illumination andobservation filters is depicted. The filter edges of the illuminationfilter 24 and of the observation filter 23 are selected so that theproduct of their transmission spectra in a small wavelength range is notzero, and is also designated as the overlap area. A small portion of theilluminating light that strikes the observed object can therefore beobserved by the observation filter 13. The observed object therefore isalso recognizable without fluorescence in (without wavelengthdisplacement) remitted blue illumination light. Fluorescence, on theother hand, appears primarily in the green and red spectral range. Thusthere is a clear color contrast between fluorescent and non-fluorescentareas of an object observed by means of the optic investigation system.

FIG. 4 is a schematic depiction of fluorescence-excitation spectra aswell as transmission spectra of illumination and observation filters,which are used for various types of fluorescence diagnostics. Thewavelength lambda is plotted on the abscissa axis. In addition to thefluorescence-excitation spectrum 81L, the transmission spectrum 83L, theillumination filter and transmission spectrum 84L of the observationfilter for PDD, the figure also shows the fluorescence-excitationspectrum 81F, the transmission spectrum 83F of the illumination filterand the transmission spectrum 84F of the observation filter forobserving autofluorescence (AF) of tissue.

In addition, FIG. 4 shows spectral sensitivities Sb, Sg, Sr of the blue,green and red color receptors of the human eye. Because cameras as faras possible are adapted to the color reception of the human eye, as arule they have similar spectral sensitivities or separate the colorchannels even more sharply. In comparing the transmission spectra 83L,83F, 84L, 84F of the illumination and observation filters for PDD and AFwith the spectral sensitivities of the color receptors of the human eye,it becomes clear that the small differences between the transmissionspectra of the illumination and observation filters for PDD and AF arerecognizable to the human eye only under good conditions in immediatecomparison—which is seldom possible.

FIG. 5 shows a schematic depiction of various products, each of atransmission spectrum of an illumination filter and of a transmissionspectrum of an observation filter. The curves are vertically slightlypushed toward one another so that they can be distinguished more easily.In fact, all products at wavelengths around 400 nm and at wavelengthsaround 500 nm are close to zero.

The product 85 of the transmission spectrum 83L of the PDD illuminationfilter and the transmission spectrum 84F of the AF observation filter isvery small or nearly zero for all wavelengths. Thus the AF observationfilter is not transparent for remitted PDD excitation light.

The product 86 of the transmission spectrum 83F of the illuminationfilter for AF diagnostics and the transmission spectrum 84L of theobservation filter for PDD is clearly greater than zero for wavelengthsin the range from about 430 nm to about 460 nm. The PDD observationfilter is thus transparent for remitted AF excitation light to a clearlyvisible degree.

The product 87 of the transmission spectrum 83L of the illuminationfilter for PDD and the transmission spectrum 84L of the observationfilter for PDD is, as already shown above with reference to FIG. 4, notzero in a small wavelength range between about a 430 nm and about 440nm. The PDD observation filter is slightly transparent for remitted PDDexcitation light.

The product 88 of the transmission spectrum 83F of the illuminationfilter for AF and the transmission spectrum 84F of the observationfilter for AF is not zero in a small wavelength range in the area of 460nm. The AF observation filter is slightly transparent for remitted AFexcitation light.

Regarding a white, non-fluorescent reference surface with an opticinvestigation system, it can thus be clearly distinguished underfavorable circumstances whether a PDD illumination filter is combinedwith an AF observation filter or an AF illumination filter is combinedwith a PDD observation filter. In the first case, an extremely darkimage is observed; in the second case, too bright an image is observedin comparison to correct combinations of illumination filter andobservation filter. It can scarcely be distinguished whether anillumination filter for PDD is combined with an observation filter forPDD or an illumination filter for AF with an observation filter for AF.In both cases the image is approximately equally bright; the differencein wavelength in any case can be distinguished by the human eye in verygood conditions in an immediate comparison.

The test method described above can be modified in such a way that theillumination filter and the observation filter can be identified as anadditional property of the optical investigation system. The followingtable shows the exposure parameter E for all possible combinations of awhite light or standard illumination (STD; first row), of a PDDillumination filter (second row) or of an AF illumination filter (thirdrow) with a standard endoscope for observing in remitted white light(first column), a PDD endoscope (second column) or an AF endoscope(third column). The standard endoscope, both in the illumination and inthe observation beam path, has a transmission that is as completelywavelength independent as possible in the wavelength range visible tothe human eye or that appears essentially not to be tinged to the humaneye. The PDD endoscope, in the observation beam path, has an observationfilter with the transmission spectrum 84L described above with referenceto FIG. 4, or the observation beam path has, without a dedicatedobservation filter, a corresponding filter characteristic. The AFendoscope in the observation beam path has an observation filter withtransmission spectrum 84F as described above with reference to FIG. 4,or the observation beam path of the AF endoscope has, without adedicated observation filter, a corresponding filter characteristic.

E STD endoscope PDD endoscope AF endoscope STD illumination 0.00230.0030 0.0033 PDD illumination 0.0020 2.50 “∞” AF illumination 0.00140.0344 2.50 

A difference that is clearly recognizable in many situations existsbetween a combination of PDD illumination and AF endoscope (exposureparameter E is very large or endless) on the one hand and the admissiblecombinations of PDD illumination and PDD endoscope or of AF illuminationand AF endoscope (in both cases the exposure parameter is approximately2.5) on the other hand. A difference, clearly recognizable as a rule,exists between the admissible combinations of PDD illumination and PDDendoscope or of AF illumination and AF endoscope on the one hand and theother combinations, in which the exposure parameter assumes values thatare clearly less than 1. The cited figures, however, are only examples,which have been measured in an individual optical investigation system.After each modification of the optical investigation system or on otheroptical investigation systems, differing values of the exposureparameter E than these can be obtained.

For an optical investigation system with a certain endoscope (eitherstandard endoscope or PDD endoscope or AF endoscope), three differentexposure parameters E are now ascertained for three different spectra ofthe excitation or illuminating light (white or standard STD; PDD; AF)and ratios are obtained for the exposure parameters E. These ratios aregiven in the following table.

STD endoscope PDD endoscope AF endoscope E_(PDD)/E_(STD) 0.84 832 “∞”E_(AF)/E_(STD) 0.61 11.5 755 E_(PDD)/E_(AF) 1.38 72.6 “∞”

It can be recognized that the three different endoscopes aredistinguishable in each of the three ratios of the exposure parameter E.In addition, by forming ratios the influence of other components of theoptical investigation system is suppressed, in particular the influenceof the light conductor cable 19, its coupling to the light source 22 andto the endoscope 10, the distance from the reference surface 72, and soon. Thus there is no further necessity for a precise positioning of thedistal end 12 of the endoscope or of the imaging device in relation tothe reference surface 72.

The test method described above can be modified as follows to identifythe endoscope used in the optical investigation system that is to betested (or its corresponding imaging device). Images of the referencesurface 72 are recorded successively with two different illuminationspectra, for example at white light illumination or without illuminationfilter and with a PDD illumination filter with the transmission spectrum83L presented above with reference to FIG. 4 in the illumination beampath. The prevailing operating conditions of the video camera 31 arerecorded for both recorded images and from them one exposure parameterE_(STD) or E_(PDD) is calculated by the aforementioned formula E=a·T·G.Finally one tests whether the ratio E_(STD)/E_(PDD) is closer to thevalue (approx. 1) necessary for a standard endoscope or closer to thevalue (approx. 800) valid for a PDD endoscope or is essentially stillgreater. If the value of the ratio E_(STD)/E_(PDD) is essentiallygreater than 800, the optical investigation system in all probabilityincludes an AF endoscope; if the ratio E_(STD)/E_(PDD) is the proximityof 800, then a PDD endoscope is present, and if the ratioE_(STD)/E_(PDD) is 1, a standard endoscope is present.

The described method is especially advantageous and, above all, can beexecuted especially rapidly if the light source apparatus 20 of theoptical investigation system provides for a mechanical replacement ofthe illumination filter 24. The method can, however, be executed, forexample, with a manual replacement of the illumination filter 24 or acorresponding exchange of complete light source apparatuses 20, eachwith firmly installed illumination filters or unchanging illuminationspectra.

Accordingly, in an optical investigation system the illumination filteror the illumination spectrum can be identified. First, images of thereference surface are recorded with two different endoscopes or with twodifferent observation filters. In the process, the prevailing operatingcondition of the video camera is recorded each time. Two exposureparameters are calculated from the operating conditions. On the basis ofthe ratios from the two exposure parameters, the illumination filter canbe identified.

Although with true endoscopy systems and other optic investigationsystems the values of the exposure parameters and their ratios scatter,the described model calculations show that the method is suitable foridentifying the observation filter or the illumination filter. Inparticular, the scattering of the measured ratio E_(x)/E_(y) is clearlysmaller than the distances of the typical values of the ratiosE_(x)/E_(y). Consequently the method is very robust.

Hereafter another variant of the test method is described with which theobservation filter and/or the illumination filter can be identified.This method can be performed in particular when the operating conditionof the video camera 31 can be recorded differentiated by color channels,that is, for example, for every color channel the exposure time and/orthe gain can be recorded separately. The method can also be executed,however, when the operating condition or the exposure time and gain arenot selected separately and cannot be recorded for every color channel,but rather, for example, are selected in common and equally for allcolor channels.

In this variant of the test method, the video camera or the cameracontrol unit independently selects exposure time, gain or otherparameters, or these parameters are prescribed from outside. Then, forevery color channel an accumulator value is selected for the recordedimage from the video camera or the camera control unit. The accumulatorvalue A_(b), A_(g), A_(r) in a color channel b, g, r is calculated, forexample, as the sum of the intensity values that are associated with theindividual image points inside a predetermined area of the image for therelevant color channel.

The following table shows in every field together the accumulator valueA_(b) for the blue color channel, the accumulator value A_(g) for thegreen color channel and the accumulator value A_(r) for the red colorchannel.

A_(b) A_(g) A_(r) STD Endoscope PDD Endoscope AF Endoscope STDillumination 728 497 227 804 992 1070 776 965 1064 PDD illumination 8573549 0 1 109 0 0 0 0 AF illumination 1862 3497 3146 40 125 236 0 0 0

For every one of the nine possible combinations of one of the threeillumination spectra with one of the three endoscopes, the ratio(A_(g)+A_(r))/A_(b) is formed by the sum of the accumulator value A_(g)for the green color channel and of the accumulator value A_(r) for thered color channel as well as from accumulator value A_(b) for the bluecolor channel. These ratios are indicated in the following table.

(A_(g) + A_(r))/A_(b) STD PDD AF STD illumination 2.17 3.94 9.40  PDDillumination 0.001 0.031 “∞” AF illumination 0.022 0.036 0.075

It can be recognized that already, with a single illumination spectrum,on the basis of the ratio (A_(g)+A_(r))/A_(b) it is possible todistinguish whether the optical investigation system includes a standardendoscope, a PDD endoscope or an AF endoscope. For this purpose, forinstance, the test method described above is modified as follows. Animage of the reference surface 72 is recorded with white lightillumination of the reference surface 72 or without illumination filter24. For each of the three color channels b, g, r, with given exposuretime and gain, the image brightness or brightness of a portion of theimage, rendered by an accumulator value ratio A_(b), A_(g), A_(r), isrecorded. The ratio (A_(g)+A_(r))/A_(b) is calculated from theaccumulator value A_(b), A_(g), A_(r). If the value of this ratio(A_(g)+A_(r))/A_(b) lies in the vicinity of 2, the optical investigationsystem includes a standard endoscope; if the quotient lies in the areaof 4, a PDD endoscope; and if the quotient lies in the area of 9, an AFendoscope.

It can also be recognized on the basis of the table that by ascertainingthe ratio Q1=(A_(g)+A_(r))/A_(b) for standard illumination and the ratioQ2=(A_(g)+A_(r))/A_(b) for PDD illumination and by division of the tworatiosx Q1 and Q2 so obtained, the endoscope present in the opticalinvestigation system can likewise be identified. If the ratio Q1/Q2 ofthe ratios for standard illumination and for PDD illumination is about2000, a standard endoscope is present; if the ratio Q1/Q2 of the ratiosis at about 100, a PDD endoscope is present; and if the ratio Q1/Q2 ofthe ratios is approximately zero, an AF endoscope is present.

If the operating condition of the video camera 31 can be recorded withdifferentiation by color channels, that is, for example for every colorchannel the exposure time and/or gain assume different values and can berecorded separately, then a corresponding process can be conducted withthe exposure parameters E_(b), E_(g), E_(r) which are associated withthe individual color channels. In the aforementioned formulas, A_(b) isreplaced in each case by E_(b), A_(g) by E_(g), and A_(r) by E_(r).

With real endoscopic or other optical investigation systems, the valuesof the exposure parameters E and of the resulting ratios vary or arescattered. Nevertheless, through these and similar algebraic linking oralso by logical linking of exposure parameters, observation filtersand/or illumination filters can be identified.

The operating condition of a video camera 31 is determined by the whitebalance parameters, among other means. Variants described below of thetest methods described in the foregoing are based on white balanceparameters as parameters of the operating condition of the video camera.

As already mentioned, the white balance serves to produce a naturalcolor impression. An image of a white or gray surface is recorded forthe white balance. The reference surface 72 of the test apparatus 40described above is suited for white balance if it is white or has anessentially wavelength independent remission factor in the spectralrange visible to the human eye. In the white balance the signals, inparticular the digital signals, are compared with one another in thethree color channels. Weighting factors are calculated for the colorchannels so that the product of the raw signal and the weighted factoris equal for every color channel. Instead of a weighted factor that isto be applied to the digital signal, the exposure times or gains can bemodified by corresponding factors.

Because only two degrees of freedom are required in order to perform awhite balance, one of the weighted factors or white balance parametersWBGb, WBGg, WBGr is not modified. According to a widely adoptedconvention, the white balance parameter WBGg is always WBGg=128=0×080.To compensate for an illumination with an excess blue portion, a whitebalance parameter WBGb<128, for example, is selected for the blue colorchannel. To compensate for an illumination with excess red portion, awhite balance parameter WBGr<128 is selected.

With fluorescence diagnostic methods, like PDD and AF diagnostics, thewhite balance is used to generate an approximately natural colorimpression despite the employed illumination and observation filters.Because of the total transmission of the illumination filter in the bluechannel, which is reduced with respect to the white light illumination,it is obvious that here white balance parameters WBGb, WBGr are selectedthat are clearly distinguished from the white balance parameters atwhite light illumination and without observation filter. Because of thedifferences between the illumination filters and between the observationfilters for PDD and for AF diagnostics as explained above with referenceto FIG. 4, the white balance parameters in these two fluorescencediagnostic methods also differ from one another. Different white balanceparameters are obtained, again, in white balance of a video camera 31 inan optical investigation system with other filter combinations.

In a schematic diagram, FIG. 6 shows typical white balance parametersafter a white balance on a white, non-fluorescent reference surface withvarious combinations of illumination filters and observation filters.The reference surface in this example is a surface of a reference bodyof white PTFE. The aforementioned white balance parameter WBGr isplotted on the abscissa, the white balance parameter WBGb on theordinate. The filter combination in each case is indicated at themeasurement points, where the indication before the plus sign refers tothe illumination filter and the indication after the plus sign to theobservation filter. Thus “STD” means no filter (white light), “POD”means a filter for PDD and “AF” a filter for AF. Admissible filtercombinations are STD+STD, PDD+PDD and AF+AF.

It can be recognized that different filter combinations have differentwhite balance parameters as a consequence, which can be unequivocallyassigned and distinguished. After conducting a white balance with anappropriate reference surface, conclusions can thus be drawn from thewhite balance parameter concerning the present filter combination.

Because the white balance parameters vary from camera type to cameratype and in some cases even from camera to camera, the white balanceparameters obtained from a white balance can, for example, be correctedby corrective parameters filed in the camera. Corrective parametersfiled in the camera are, for example, white balance parameters obtainedon a white surface without illumination and observation filter. Thesecorrective parameters can be filed in the camera control device 35instead of in the camera 31. Additional corrections can ensue for thestructural form or the type of endoscope, because rigid and flexibleendoscopes, endoscopes with different diameters or for differentapplications have different transmission spectra in the illuminationbeam path and in the observation beam path.

In using a non-white reference surface for a white balance, theprecision or reliability of the differentiation of various filtercombinations can be further improved on the basis of the white balanceparameters. This is true in particular when areas of the referencesurface comprise materials whose absorption or fluorescence excitationspectra have edges or flanks in the proximity of the filter edges of theillumination and observation filters that are to be differentiated.

In a schematic diagram, FIG. 7 shows white balance parameters forvarious filter combinations in a white balance on a reference surfacemade up of a covering layer of Maragloss GO 320 Fluoresco Yellow paintproduced by Marabu. Abscissa and ordinate as well as designations ofmeasured values correspond to those of FIG. 6. A comparison of FIGS. 6and 7 shows that an especially secure identification of the existingfilter combination is possible if both the white balance parameters froma white balance on a Teflon surface and the white balance parametersfrom a white balance on a covering layer of Marabu Maragloss GOFluoresco 320 yellow are involved. Additional improvements are alsopossible, for example, by a logical or algebraic linking of the whitebalance parameters.

In a variant of the test method described above, after a white balanceof the video camera 31 on the reference surface 72, the white balanceparameters are read out or recorded as parameters of the operatingcondition of the video camera 31. The illumination filter 24 and theobservation filter 13 are identified on the basis of the white balanceparameters. The illumination filter and the observation filter can beidentified even more securely if one of the two filters is already knownor if the white balance is conducted successively on reference surfacesor areas of a reference surface with different optical properties.

White balance parameters—assuming linear behavior of the videocamera—are independent of absolute brightness because they only describeproportions between signals in the individual color channels. Thus thewhite balance parameters ascertained in a white balance are alsoindependent of the distance between the distal end 12 of the imagingdevice 10 and the reference surface 72. Therefore, in this variant ofthe test method, there is no longer a necessity for a precisepositioning of the distal end 12 of the endoscope or of the imagingdevice in relation to the reference surface 72.

FIG. 8 shows a schematic flow diagram of a method for testing an opticalinvestigation system, with a light source, an imaging device and a videocamera for optical investigation of an object. Although the method isapplicable also in optical investigation systems and test apparatusesthat differ from the one presented above with reference to FIGS. 1 and2, hereinafter for the sake of simplicity of understanding, referencenumbers from FIGS. 1 and 2 are used by way of example. The method caninclude characteristics of the test method described above and of itsdescribed variants. In particular, the method can be a combination ofseveral described variants.

In an optional first step 101, an expected application of the opticalinvestigation system is recorded, for example on a user interface aftera corresponding request. In an optional second step 102, a requirementassociated with the expected application is ascertained on an operatingcondition of the video camera 31 of the optical investigation system,for example by reading out a look-up table. One or more requirements forthe operating condition of the video camera 31 can alternatively bepre-established without modification.

In a third step 103, a distal end 12 of an imaging device 10, inparticular of an endoscope, is inserted through an aperture 43 into ahollow space 42 in a light-insulated housing 41. In an optional fourthstep 104, which can be executed immediately after the third step 103 orsimultaneously with it, the distal end 12 of the imaging device 10 ispositioned in a predetermined position and direction in relation to areference surface 72 positioned in the hollow space 42. This occurs, forexample, with support from a positioning device 50, which guides theimaging device 10, in particular its distal end 12, and/or holds it byform-locking or force-locking. As already mentioned above, the fourthstep 104 can be omitted, for example, if ratios of exposure parametersor accumulator values are formed successively or white balanceparameters are observed, because in that way the influence of thedistance and of the precise positioning of the distal end 12 of theimaging device 10 relative to the reference surface can be almosteliminated.

In a fifth step 105, the reference surface 72 is illuminated withilluminating light with an illumination spectrum. If the imaging deviceis an endoscope 10, the illumination occurs in particular by means ofthe endoscope or by means of an illumination beam path in the endoscope10. In an optional sixth step 106, a white balance is conducted, asdescribed above, while the reference surface is illuminated. In theprocess, white balance parameters WBGr, WBGb, for example, are selected.

In a seventh step 107, an image is recorded by a video camera 31 duringthe illumination of the reference surface 72 by the imaging device 10.In an eighth step 108, the operating condition of the video camera 31that is present during the seventh step 107 is recorded, in particularread out from the video camera 31 or the camera control device 35.Alternatively a noise level or a signal-noise distance in the recordedimage, for example, is determined, from which conclusions can be drawnconcerning the operating condition of the video camera 31. The operatingcondition of the video camera includes, for example, white balanceparameters WBGr, WBGb, an exposure time valid for all color channels, again valid for all color channels, exposure times and gains valid forindividual color channels, or accumulator values valid for individualcolor channels.

In an optional ninth step 109, an exposure parameter is ascertained, andin particular calculated, from the recorded operating condition of thevideo camera. In a tenth step 110, the ascertained exposure parameter oran algebraic or logical linking of exposure parameters or of accumulatorvalues is compared with one or more threshold values that are associatedwith an expected application or apply overall to it. Alternatively or inaddition, the operating condition of the video camera or the parametersthat characterize it are compared with other requirements associatedwith the predetermined application of the optical investigation systemand applying overall to it. The result of the comparison indicates thefunctionality or another property of the optical investigation system.

In an optional eleventh step 111, a report is issued that can include astatement on the functionality of the optical investigation system, anoperating recommendation and/or an operating instruction. In a twelfthstep 112, which can also be conducted at any other point in the process,patient data are recorded, for example by means of a user interface. Inan optional thirteenth step 113, the patient data, the result of thetest method with respect to the functionality or another property of theoptical investigation system, and optionally the result of a succeedingor ongoing investigation of a patient are filed in a database by meansof the optical investigation system.

In addition, model designations, series numbers, software or firmwareversions and other data on components of the optical investigationsystem can be requested over a communication line 39 and filed in thedatabase for documentation or logging. In addition, in the database orseparately on another data carrier, the investigation of the patient canbe documented or logged. Here images or a video data stream from thecamera 31, for example, is filed in the database (for example in MPEGformat) or on a videotape.

1. A method for testing an optical investigation system, with an imagingdevice, a video camera and a light source for optical investigation ofan object, with the following steps: illuminate a reference surface withpredetermined optical properties with illuminating light from the lightsource; record an image of the reference surface by means of the imagingdevice and video camera; record an operating condition of the videocamera that prevails during the recording of the image; determine thefunctionality or another property of the investigation system on thebasis of the recorded operating condition.
 2. A method according toclaim 1, in addition with the following step: position the distal end ofthe imaging device at a predetermined position in relation to thereference surface.
 3. The method according to claim 1, in addition withthe following steps: record an expected application of the opticalinvestigation system; ascertain a requirement that is associated withthe expected application of the optical investigation system, so thatthe functionality for the expected application or another predeterminedproperty of the optical investigation system is present if the operatingcondition corresponds to the requirement.
 4. The method according toclaim 1, wherein the reference surface is illuminated with an irradiancethat equals a predetermined fraction of the irradiance applied in theexpected use of the optical investigation system.
 5. The methodaccording to claim 1, wherein: the step of recording the operatingcondition includes ascertaining an exposure parameter; the step ofdetermining the functionality or another property includes comparing theascertained exposure parameter with a predetermined threshold value. 6.The method according to claim 1, wherein: the step of illuminatingsuccessively includes illuminating the reference surface withilluminating light with a first spectrum and illuminating the referencesurface with illuminating light with a second spectrum; a firstoperating condition of the video camera that prevails during therecording of an image while illuminating the reference surface withilluminating light with the first spectrum is recorded; a secondoperating condition of the video camera that prevails during therecording of an image of the illumination of the reference surface withilluminating light with the second spectrum is recorded; thefunctionality or the other property is determined on the basis of thefirst operating condition and of the second operating condition.
 7. Themethod according to claim 1, wherein the step of determining thefunctionality or another property includes the following steps:ascertain an indicator parameter from the recorded first operatingcondition and the recorded second operating condition; compare theascertained indicator parameter with a threshold value.
 8. The methodaccording to claim 1, wherein the recording of an operating conditionincludes ascertaining one exposure parameter for each of a number ofcolor channels.
 9. The method according to claim 1, wherein therecording of an operating condition includes recording a white balanceparameter.
 10. The method according to claim 1, wherein the recording ofan operating condition includes a noise level or a signal-noise distancein the recorded image
 11. The method according to claim 1, in additionwith the following steps: record patient data; file information on thefunctionality or the other property as well as the patient data in adatabank. 12-13. (canceled)
 14. A computer readable storage mediumincluding a set of instructions executable by a processor for testing anoptical investigation system, the set of instructions operable to:illuminate a reference surface with predetermined optical propertieswith illuminating light from a light source; record an image of thereference surface by means of an imaging device and video camera; recordan operating condition of the video camera that prevails during therecording of the image; determine the functionality or another propertyof the investigation system on the basis of the recorded operatingcondition.
 15. A control device for an optical investigation comprising:a light source, said light source illuminating a reference surface withpredetermined optical properties; a video camera; an imaging device;said video camera and said imaging device recording an image of saidreference surface; a memory, said memory storing an operating conditionof said video camera that prevails during the recording of the image;and a processor, said processor determining the functionality or anotherproperty of the investigation system from said operating condition.